BIOL 1104 Lecture Notes - Lecture 20: Cambrian Explosion, Molecular Clock, Hox Gene
20 Apr 2020
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Document Summary
As a rule, animals are multicellular, heterotrophic eukaryotes with tissues that develop from embryonic layers but . There are exceptions to nearly every criterion for distinguishing animals from other life-forms. Several characteristics, taken together, sufficiently define the group. The ediacaran biota are the oldest known assemblage of large multicellular organisms. They lived 600 to 535 million years ago. Some ediacaran animals appear to be sponges and cnidarians but. Must have been heterotrophs because they lived bottom of oceans most don"t appear to be closely related to living animals where no light goes. The cambrian explosion (535 to 525 million years ago) marks the earliest fossil appearance of many major groups of living animals. The cambrian is the origin of animal complexities; where they became more complex. The earliest signs of vertebrates are from the cambrian. Molecular clock puts the origin of animals long before the cambrian.
